Iran began mass-producing two high-speed variants of missile-launching assault boats on Monday, warning its enemies not to "play with fire" as it boosts security along its coastline.

The inauguration of the production lines for the Seraj and Zolfaqar speedboats comes a day after President Mahmoud Ahmadinejad unveiled Iran's home-built bomber drone, which he said would deliver "death" to Iran's enemies.

The United States expressed concern about the Islamic republic's growing military capabilities.

Iran's state news agency IRNA reported that the Seraj (Lamp) and Zolfaqar (named after Shiite Imam Ali's sword) boats would be manufactured at the marine industries complex of the defence ministry.

Defence Minister Ahmad Vahidi opened the assembly lines, saying the vessels would help to strengthen Iran's defences, IRNA said.

"Today, the Islamic Republic of Iran is relying on a great defence industry and the powerful forces of Sepah (Revolutionary Guards) and the army, with their utmost strength, can provide security to the Persian Gulf, the Sea of Oman and Strait of Hormuz," Vahidi said.

He issued a stern warning to Iran's foes.

"The enemy must be careful of its adventurous behaviour and not play with fire because the Islamic Republic of Iran's response would be unpredictable," IRNA quoted him as saying.

"If enemies attack Iran, the Islamic Republic of Iran's reaction will not be restricted to one area. The truth of our defence doctrine is that we will not attack any country and that we extend our hand to all legitimate countries."

Iran's arch-foes, the United States and Israel, have not ruled out taking military action over Tehran's controversial nuclear programme.

"This is... something that is of concern to us and... concern to Iran's neighbours," State Department spokesman Philip Crowley told reporters in Washington of Iran's latest military acquisitions.

He said that while all nations had the right to self-defence, the United States "take into account... systems that can potentially... threaten particular countries or peace and stability in the region."

Faced with "the growth Iran's capabilities over a number of years, we've stepped up our military cooperation with other countries in the region," Crowley said.

Iran has in the past threatened to close the Strait of Hormuz, choking off some 40 percent of tanker-shipped oil worldwide, in the event of a military attack.

IRNA said Zolfaqar was a new generation missile-launching vessel.

"It is designed for quick assaults on ships and is equipped with two missile launchers, two machine guns and a computer system to control the missiles," the report said.

Fars news agency cited Vahidi as saying that Zolfaqar was to be equipped with the Nasr 1 (Victory) marine cruise missile "which has high destructive power."

Iran has previously said that the Nasr missile can destroy targets weighing up to 3,000 tonnes.

IRNA said Seraj, designed for a tropical climate, was also a swift assault vessel for use in the Caspian sea, the Gulf and the Gulf of Oman, adding that it can also fire rockets.

"Seraj is a fast-moving assault rocket launcher using sophisticated and modern technology," Vahidi was cited as saying by IRNA.

The launch of the production lines comes as Iran marks its annual "government week," when it traditionally showcases its latest technological achievements.

The naval commander of Iran's elite Revolutionary Guards, Ali Fadavi, was quoted by IRNA as saying that the missile-launching boats are the world's fastest.

"The Iranian-made missile-launching boats rank first in the world when it comes to their velocity," he said.

Ahmadinejad on Sunday unveiled a bomber drone with a range of up to 1,000 kilometres (620 miles), which he dubbed the "ambassador of death."

State media said the drone, Karar (Assailant), can carry four stealth cruise missiles, two bombs of 250 pounds (115 kilos) each or a precision missile of 500 pounds (230 kilos).

Tehran on Friday test-fired a surface-to-surface missile named Qiam (Rising), and more announcements are expected over the next few days, including the test-firing of a third-generation Fateh (Conqueror) 110 missile.

Iran also recently took delivery of four domestically built Ghadir mini-submarines, stealth vessels designed to operate in shallow waters such as the Gulf.

burs/srm